Many ion generating devices that utilize a discharge phenomenon have been put into practical use. These ion generating devices generally include an ion generating unit for generating ions, a high-voltage transformer for supplying a high voltage to the ion generating unit, a high-voltage transformer drive circuit for driving the high-voltage transformer, and a power supply input portion such as a connector.
Ion generating units may be roughly categorized into two types. One type uses a metal wire, a metal plate having an acute portion, a needle-shaped metal part, etc., as a discharge electrode and a metal plate, a grid, etc., at a ground potential as a counter electrode. The counter electrode may be omitted when the ground is used as a counter electrode. In this type of ion generating unit, air serves as an insulator. When a high voltage is applied between the electrodes of the ion generating unit, an electric field concentration occurs at the tip of the electrode having an acute portion and electrical breakdown of air occurs in the immediate vicinity of the tip, so that a discharge phenomenon is produced.
The other type includes a pair of electrodes, which are an induction electrode embedded in a high-breakdown-voltage dielectric and a discharge electrode disposed on a surface of the dielectric. When a high voltage is applied between the electrodes of the ion generating unit of this type, an electric field concentration occurs in the vicinity of an outer edge portion of the discharge electrode on the surface of the dielectric and electrical breakdown of the air occurs in the vicinity of the outer edge portion, so that a discharge phenomenon is produced.
Japanese Unexamined Patent Application Publication No. 2002-374670 (see PTL 1) describes an example of an ion generating device according to the related art. This ion generating device is of the type which includes a discharge electrode as an ion generating electrode and includes no counter electrode. In this ion generating device, a piezoelectric transformer that supplies a high voltage to the ion generating electrode and a drive circuit for driving the piezoelectric transformer are mounted in a casing in an integrated manner through molding. The ion generating electrode is disposed outside the casing and connected to a cable that extends from the inside of the casing.
Japanese Unexamined Patent Application Publication No. 2008-016345 (see PTL 2) discloses a structure of an ion generating device whose thickness is reduced by two-dimensionally arranging an ion generating unit, a transformer drive circuit, and a transformer in a casing and disposing the transformer separately from a circuit board.